This lecture describe how the routing from source to destination works.

1. Computer Networks
CS-605

2. Routing
• Routing is the process of moving packets across a
network from one host to a another.
• It is usually performed by dedicated devices called
routers.
• Packets are the fundamental unit of information
transport in all modern computer networks, and
increasingly in other communications networks as well.

3. Routing Table
• A routing table is a set of rules, often viewed in
table format, that is used to determine where
data packets traveling over an Internet Protocol
(IP) network will be directed.
• All IP-enabled devices, including routers and
switches, use routing tables.

4. Entries of an IP Routing Table
• A routing table contains the information necessary to
forward a packet along the best path toward its destination.
• Each packet contains information about its origin and
destination.
• Routing Table provides the device with instructions for
sending the packet to the next hop on its route across the
network.

5. Entries of an IP Routing Table
• Each entry in the routing table consists of the following entries:
 Network ID: The network ID or destination corresponding to the route.
 Subnet Mask: The mask that is used to match a destination IP address to the
network ID.
 Next Hop: The IP address to which the packet is forwarded.
 Outgoing Interface: Outgoing interface the packet should go out to reach the
destination network.
 Metric: A common use of the metric is to indicate the minimum number of hops
(routers crossed) to the network ID.

6. Routing Protocols

7. Routing Protocols
 Routing protocols are the set of rules used by the routers to communicate
between source & destination.
 They do not move the information source to destination only update the routing
table.
 Each protocol has its own algorithm to choose the best path.
 The metrics by routing protocols:-
• Number of network layer devices along with the path
• Bandwidth
• Delay
• Load

8. Static Routing Protocols
 Static routing, when an administrator manually assigns the
path from source to destination network.
 This is feasible in small networks, but not in large networks.

Advantages:-
– No overhead on router CPU.
– No bandwidth usage between links.
– Security (only administrator add routes.)

Disadvantages:-
– All link will be down on a link failure.
– Not practical on large networks.
– Administrator must update all routes.

9. Default Routing Protocols
 Default route is use when no specific route can be
determined for a given Internet Protocol (IP) destination
address.
 All packets for destinations not established in the routing
table are sent via the default route.

10. Dynamic Routing Protocols
 Dynamic routing is a networking technique that provides optimal data
routing. Unlike static routing, dynamic routing enables routers to select
paths according to real-time logical network layout changes.
Advantages
– Less work in maintaining the configuration when adding & deleting
networks.
– Protocols automatically react to the topology changes.
Disadvantages
– Routers resource are used.
– More administrator knowledge is required for configuration.